This invention relates to a lap edge sealant composition for sealing the lap joints of roofing materials, and more particularly, to a lap edge sealant having a high solids content and a low volatile organic compound (VOC) content.
In the field of single-ply commercial rubber roofing, sheets of roofing material are typically laid on a roof in an overlapping fashion and spliced together to form a continuous sheet which covers the roof. Lap joints are typically used to splice adjacent sheets of roofing material together. The exposed scams of the lap joints are then sealed with an adhesive, typically, a caulking compound, to act as an additional seal to prevent penetration of moisture along the external seam. Currently, solvent-based adhesive sealants are used for sealing the lap joints of adjacent sheets of membrane roofing materials. Such sealants typically utilize aromatic solvents such as benzene, toluene, xylene, etc. However, such solvent-based sealants are environmentally undesirable as they typically contain over 350 grams per liter (3 pounds per gallon) of volatile organic compounds. Because of environmental concerns, many states are beginning to mandate products having no more than 250 grams per liter (2 pounds per gallon) of volatile organic compound (VOC) content.
Another disadvantage of solvent-based sealants currently in use is their low solids content, i.e., about 20 to 30%. As such sealants typically cure by solvent evaporation, high shrinkage (typically about 40-60%) can occur when using these sealants. As a consequence, the cured films may exhibit fissure-type cracking and degradation after long term outdoor exposure.
A number of adhesives have been developed which exhibit lower VOC levels. For example, Congelio et al., U.S. Pat. No. 5,817,708, teach a low VOC content (less than 250 g/l) solvent-based adhesive for use in joining thermoplastic materials. Patel et al., U.S. Pat. No. 5,495,040, also teaches a low VOC (less than 250 g/l) solvent-based adhesive for joining ABS molded articles. However, such adhesives are not specifically formulated for use as lap edge roofing sealants, nor do they have a high solids content.
Backenstow et al., U.S. Pat. No. 4,849,268 teach a 100% solids sealant for providing an internal seal to spliced roofing membranes which is formed from EPDM, butyl or silicone based caulking compositions. The sealant is applied in combination with a splicing cement to the internal portion of the splice. However, Backenstow et al. require that the sealant, splicing cement, and roofing membrane be compatible in order to avoid separation of the sealant from the cement. In addition, Backenstow et al. do not seal the exterior seam on the lap joint.
Accordingly, there is still a need in the art for a lap edge sealant which effectively seals the external lap joints of adjacent sheets of membrane roofing material, which has a high solids content, a low VOC content, and which exhibits low shrinkage upon curing.